This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The RBC membrane is not a static but a metabolically regulated active structure. It is known that biochemical energy controls its static and dynamic characteristics. The presence of ATP is not only crucial in maintaining the biconcave shape of the RBC membrane, but was also shown to increase the dynamic membrane fluctuations. However, the regulatory mechanism of ATP in RBC membranes still remains elusive. We investigate the effects of ATP by measuring the morphologies and membrane dynamics of RBC using the quantitative phase microscopes we developed.